I just bought it, and I must say it is a very nice, slick, modern Mac app. I prefer it to chatting in Adium so far.
That said, I would like it much more if it supported more services than just XMPP. Supporting the Adium service plugin API would actually be a really nice way of doing this (from a user's perspective), but if not, a new API would do well also.
Hi there, I'm the developer of Flamingo. This is something that I considered during the development process but with the Mac App Store, sandboxing, and the overall difficulty of designing a good plugin API, this didn't make the cut for 1.0. Once things stabilize a bit I'll have more time to experiment with things like this. It's only 1.0 :)
When I first read the features, I assumed the Facebook/Hangouts and XMPP were essentially 3 different modules, which would probably make extending it to third party plugins fairly easy. But I realised that all of the services are XMPP at the moment, and therefore I suppose this would mean adding lots more abstraction to internal APIs and stuff.
I've heard about issues with sandboxing and plugins before, but as far as I can tell they are mostly for when plugins need access to the filesystem, as they have a different bundle ID and therefore don't get permissions from the main application? I might be completely wrong there though. As long as the plugins for Flamingo don't need filesystem access, or other privileged access, I would have thought it would be fine. RapidWeaver, for example, has a large plugin community, but is distributed on the App Store.
That said, I would like it much more if it supported more services than just XMPP. Supporting the Adium service plugin API would actually be a really nice way of doing this (from a user's perspective), but if not, a new API would do well also.